Energy in Chemical Reactions unit
Which reaction is endothermic?
6CO2 + 12H2O + energy→C6H12O6 + 6O2 + 6H2O
Which reaction is exothermic?
CH4 + 2O2→CO2 + 2H2O + 891 kJ
Which statement is correct about the law of conservation of energy?
Energy is transferred when atoms are rearranged.
Two metal blocks that have slightly different temperatures are placed next to one another. After five minutes, they both have lower but equal temperatures. According to the law of conservation of energy, what most likely happened?
Energy was transferred from the warmer block to the cooler block.
Which statement best describes the direction of heat flow by conduction between two samples of the same material?
Heat flows from faster molecules to slower molecules when they collide.
A student touches a freshly baked cake that was taken out of the oven. Which best explains why the cake feels hot?
Molecules in the cake are moving faster than molecules in the skin.
A baker touches a pie right after taking it out of the oven. Which statement best explains why the pie feels hot?
Molecules in the pie move faster than molecules in the skin, so heat is transferred to the skin.
Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true?
The gas molecules in both containers have the same average kinetic energy.
An arrow is fired at a target on a high wall. How does the energy change between the moment the arrow is fired and the moment it hits the target?
The kinetic energy decreases as potential energy increases.
The temperature of a sample of liquid water changes from 50°C to 30°C. Which statement best explains the change that must happen at the molecular level?
The molecules move more quickly and their average kinetic energy decreases.
In what type of reaction or process does heat flow into the system?
endothermic
Which is the best term to use when describing the energy of motion?
kinetic
Which is the best term to use when describing the energy of position?
potential
Which energy change best relates to a boulder that is rolling down the side of a hill?
potential energy transforming into kinetic energy
Thermal energy is the energy associated with
temperature
Which direction does thermal energy flow in the following diagram? holding an ice cream cone
Heat flows from the hand to the ice cream.
Heat that flows by conduction is the transfer of thermal energy between substances in contact. What must occur for this to happen?
One system must have higher kinetic energy than the other system.
The temperature of a gas is increased. Which statement best explains the effect that this has on the motion of gas particles?
The average kinetic energy increases, and the particles collide more frequently.
Two samples of carbon come into contact. A heat transfer will occur between sample A and sample B. What must be true for heat to transfer from sample A to sample B?
The average kinetic energy of A is greater than that of B.
Which is the best example of how electromagnetic energy is used in everyday life?
a patient receiving an X-ray in a hospital
Which answer defines exothermic reaction?
a process in which energy is released as heat
How should the baking of a pizza be categorized?
as an endothermic process because the dough releases heat
A welding torch produces a flame by burning acetylene fuel in the presence of oxygen. This flame is used to melt a metal. Which energy transformation represents this process?
chemical energy into thermal energy
Which best describes heat?
energy that flows from a hot mug of tea to a cold hand
A baseball player hits a ball. Which is the best description of the energy of the ball as it flies over the pitcher's head?
kinetic
